bisync: account for differences in backend features on integration tests - see #5679

Before this change, integration tests often could not be run on backends with
differing features from the local system that goldenized them. In particular,
differences in modtime precision, checksum support, and encoding would cause
false positives. After this change, the tests more accurately account for the
features of the backend being tested, which allows us to see true positives
more clearly, and more meaningfully assess whether a backend is supported.

cmd/bisync/checkfn.go

@@ -107,6 +107,9 @@ func CryptCheckFn(ctx context.Context, dst, src fs.Object) (differ bool, noHash
 	}
 	if cryptHash != underlyingHash {
 		err = fmt.Errorf("hashes differ (%s:%s) %q vs (%s:%s) %q", fdst.Name(), fdst.Root(), cryptHash, fsrc.Name(), fsrc.Root(), underlyingHash)
+		fs.Debugf(src, err.Error())
+		// using same error msg as CheckFn so integration tests match
+		err = fmt.Errorf("%v differ", hashType)
 		fs.Errorf(src, err.Error())
 		return true, false, nil
 	}